WM8976 datasheet(69/83 Pages) WOLFSON

69 / 83 page

Preliminary Technical Data

WM8976

PTD Rev 2.0 February 2005

SDIN

SCLK

1st register data bit

DEVICE ADDRESS

(7 BITS)

RD / WR

BIT

ACK

(LOW)

CONTROL BYTE 1

(BITS 15 TO 8)

CONTROL BYTE 1

(BITS 7 TO 0)

remaining 8 bits of

STOP

START

ACK

(LOW)

ACK

(LOW)

Figure 39 2-Wire Serial Control Interface

In 2-wire mode the WM8976 has a fixed device address, 0011010.

RESETTING THE CHIP

The WM8976 can be reset by performing a write of any value to the software reset register (address

0 hex). This will cause all register values to be reset to their default values. In addition to this there

is a Power-On Reset (POR) circuit which ensures that the registers are set to default when the

device is powered up.

POWER SUPPLIES

The WM8976 can use up to four separate power supplies:

AVDD and AGND: Analogue supply, powers all analogue functions except the speaker output and

mono output drivers. AVDD can range from 2.5V to 3.6V and has the most significant impact on

overall power consumption (except for power consumed in the headphone). A large AVDD slightly

improves audio quality.

SPKVDD and SPKGND: Headphone and Speaker supplies, power the speaker and mono output

drivers. SPKVDD can range from 2.5V to 5V. SPKVDD can be tied to AVDD, but it requires separate

layout and decoupling capacitors to curb harmonic distortion. With a larger SPKVDD, louder

headphone and speaker outputs can be achieved with lower distortion. If SPKVDD is lower than

AVDD, the output signal may be clipped.

DCVDD: Digital core supply, powers all digital functions except the audio and control interfaces.

DCVDD can range from 1.8V to 3.6V, and has no effect on audio quality. The return path for DCVDD

is DGND, which is shared with DBVDD.

DBVDD Can range from 1.8V to 3.6V. DBVDD return path is through DGND.

It is possible to use the same supply voltage for all four supplies. However, digital and analogue

supplies should be routed and decoupled separately on the PCB to keep digital switching noise out

of the analogue signal paths.

RECOMMENDED POWER UP/DOWN SEQENCE

In order to minimise output ‘pop’ and ‘click’ noise it is recommended that the device is powered up in

a controlled sequence.

In addition to this it is recommended that the zero cross functions are used when changing the

volume in the PGAs.

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